1. Field of the Invention
The present invention relates to a transflective liquid crystal display (LCD) panel and a pixel structure thereof, and more particularly, to a transflective LCD panel with a single gap and a pixel structure thereof.
2. Description of the Prior Art
Most LCDs can be categorized into three kinds: the transmissive type, the reflective type, and the transflective type according to their light source. The transmissive LCD uses backlight as a source for emitting light. The light emitted by the backlight will pass through the LCD panel to let an user see the image displayed on the LCD panel. The reflective LCD has a reflective pixel electrode. When displaying the image, the ambient light will enter the LCD from the user side and then be reflected by the reflective pixel electrode. The reflected light will pass through the reflective LCD panel again, and finally the user can see the image displayed on the LCD. The transflective LCD panel has the LCD both of transmissive type and reflective type. In other words, each pixel area of the transflective LCD panel comprises a transmission region and a reflection region.
Generally, a traditionally transflective LCD panel has an array substrate, a color filter substrate, and a liquid crystal layer disposed between the two substrates. The transflective LCD panel further includes pluralities of pixel areas, and each of the pixel areas comprises a reflection region and a transmission region, while each reflection region and each transmission region has a reflective pixel electrode and a transmission pixel electrode respectively. Because the transmission region of the transflective LCD panel uses a backlight as its light source, the light will pass through the liquid crystal layer only once. However, the reflection region uses the ambient light as a light source, so that the light will pass through the liquid crystal layer twice. In such a case, the optical path-length difference in the reflection region is twice as much as that in the transmission region, such that the relation of reflectance versus voltage mismatches the relation of transmittance versus voltage (i.e. gamma curve) while driving the liquid crystal (LC) molecules.
For this reason, manufacturers have designed a transflective LCD panel having a dual cell gap to solve the problem of mismatching driving voltage. More specifically, in this kind of transflective LCD panel, a dielectric layer is disposed under the reflective pixel electrode so as to adjust a cell gap of the reflection region. By disposing the dielectric layer, the cell gap of the liquid crystal layer in the reflection region is smaller than the cell gap in the transmission region, so that the optical path-length difference of light passing through the reflection region is the same as that of light passing through the transmission region. However, although the problem of mismatching driving voltage may be solved through the above-mentioned design of dual gap by adjusting the optical path-length difference in the transflective LCD panel, an obvious height difference of the border between the reflection region and the transmission region will make the LC molecules difficult to align, thereby resulting in light leakage and lowering the quality of displayed images. Furthermore, the step of fabricating the dielectric layer in the reflection region increases the fabrication cost and decreases yield.
On the other hand, in order to solve the mismatching problem of gamma curves of the transmission mode and the reflection mode of the transflective LCD panel, manufacturers have also develop an adjusted capacitance coupling (ACC) technique, by the way of disposing a first common electrode, a second common electrode, a first coupling capacitor (CC), and a second coupling capacitor (C2) in the transflective LCD panel to change the voltage difference of the reflection region through the coupling of the first coupling capacitor and the second coupling capacitor, so as to adjust the gamma curve of the reflection type to match the gamma curve of the transmission type. However, in the device arrangement of the current ACC technique design, the additional second common electrode crosses the data line on the array substrate such that the voltage of the second common electrode will be affected when a signal is transferred through the data line to the pixels of the display panel, resulting in serious cross-talk problem, which cannot meet the requirement of product standard that the cross-talk has to be less than 2%. As a result, the current ACC transflective LCD panel with a single gap still has an apparent disadvantage of serious cross-talk and cannot display high-quality images for meeting the product standards.